Re: [PATCH net-next V2 00/11] net/mlx5e: Add support for devmem and io_uring TCP zero-copy

Stanislav Fomichev
2025-05-28T15:45:05Z

On 05/28, Dragos Tatulea wrote:
> On Tue, May 27, 2025 at 09:05:49AM -0700, Stanislav Fomichev wrote:
> > On 05/23, Tariq Toukan wrote:
> > > This series from the team adds support for zerocopy rx TCP with devmem
> > > and io_uring for ConnectX7 NICs and above. For performance reasons and
> > > simplicity HW-GRO will also be turned on when header-data split mode is
> > > on.
> > >
> > > Find more details below.
> > >
> > > Regards,
> > > Tariq
> > >
> > > Performance
> > > ===========
> > >
> > > Test setup:
> > >
> > > * CPU: Intel(R) Xeon(R) Platinum 8380 CPU @ 2.30GHz (single NUMA)
> > > * NIC: ConnectX7
> > > * Benchmarking tool: kperf [1]
> > > * Single TCP flow
> > > * Test duration: 60s
> > >
> > > With application thread and interrupts pinned to the *same* core:
> > >
> > > |------+-----------+----------|
> > > | MTU | epoll | io_uring |
> > > |------+-----------+----------|
> > > | 1500 | 61.6 Gbps | 114 Gbps |
> > > | 4096 | 69.3 Gbps | 151 Gbps |
> > > | 9000 | 67.8 Gbps | 187 Gbps |
> > > |------+-----------+----------|
> > >
> > > The CPU usage for io_uring is 95%.
> > >
> > > Reproduction steps for io_uring:
> > >
> > > server --no-daemon -a 2001:db8::1 --no-memcmp --iou --iou_sendzc \
> > > --iou_zcrx --iou_dev_name eth2 --iou_zcrx_queue_id 2
> > >
> > > server --no-daemon -a 2001:db8::2 --no-memcmp --iou --iou_sendzc
> > >
> > > client --src 2001:db8::2 --dst 2001:db8::1 \
> > > --msg-zerocopy -t 60 --cpu-min=2 --cpu-max=2
> > >
> > > Patch overview:
> > > ================
> > >
> > > First, a netmem API for skb_can_coalesce is added to the core to be able
> > > to do skb fragment coalescing on netmems.
> > >
> > > The next patches introduce some cleanups in the internal SHAMPO code and
> > > improvements to hw gro capability checks in FW.
> > >
> > > A separate page_pool is introduced for headers. Ethtool stats are added
> > > as well.
> > >
> > > Then the driver is converted to use the netmem API and to allow support
> > > for unreadable netmem page pool.
> > >
> > > The queue management ops are implemented.
> > >
> > > Finally, the tcp-data-split ring parameter is exposed.
> > >
> > > Changelog
> > > =========
> > >
> > > Changes from v1 [0]:
> > > - Added support for skb_can_coalesce_netmem().
> > > - Avoid netmem_to_page() casts in the driver.
> > > - Fixed code to abide 80 char limit with some exceptions to avoid
> > > code churn.
> >
> > Since there is gonna be 2-3 weeks of closed net-next, can you
> > also add a patch for the tx side? It should be trivial (skip dma unmap
> > for niovs in tx completions plus netdev->netmem_tx=1).
> >
> Seems indeed trivial. We will add it.
>
> > And, btw, what about the issue that Cosmin raised in [0]? Is it addressed
> > in this series?
> >
> > 0: https://lore.kernel.org/netdev/9322c3c4826ed1072ddc9a2103cc641060665864.camel@nvidia.com/
> We wanted to fix this afterwards as it needs to change a more subtle
> part in the code that replenishes pages. This needs more thinking and
> testing.

Thanks! For my understanding: does the issue occur only during initial
queue refill? Or the same problem will happen any time there is a burst
of traffic that might exhaust all rx descriptors?